A method for combining data packets uses a telecommunication device, whereby a first data packet comprising a first retransmission number being received by the telecommunication device on a telecommunication channel and the next data packet being received by the telecommunication device on the telecommunication channel is a second data packet comprising a second retransmission number at a delay time dt after the first data packet.
Such methods are known from the art. In communication systems often packet transmission is employed. One example of such a transmission system is the so called E-DCH scheme (E-DCH: Enhanced Dedicated Channel, basically an improvement of the existing UMTS uplink channel) which is right now being standardized as an enhancement of the UMTS system (UMTS: Universal Mobile Telecommunication System).
The outlines of the E-DCH scheme can be found in the 3GPP RAN 1 technical report TR 25.89 v2.0.0 “Feasibility Study for Enhanced Uplink for UTRA FDD (Release 6)”, R1-040392, February 2004, Malaga, Spain.
This scheme is designed to make use of a HARQ (HARQ: Hybrid ARQ, Hybrid Automated Retransmission reQuest) scheme. In this scheme packets are transmitted, and if they are not received correctly, a retransmission is transmitted. At the receiver both the initial transmission and the retransmission is taken together to decode the packet. This gives a better performance, as if only the retransmission would be used without regarding previous transmissions (non-hybrid ARQ).
Within this scheme should be made sure, that both received transmissions actually relate to the same transmitted (higher layer) packet i.e. both transmissions are derived from the same information content, the same “higher layer” packet (but may be transmitted using different packets on layer 1).
There are several ways to ensure this: one is a so called synchronous retransmission protocol. In this protocol a retransmission is sent at a fixed time interval after the initial transmission, or the previous retransmission. In this way the receiver knows at which times to expect retransmissions of a given packet. However, the receiver still does not know, whether two transmissions at compatible times in fact relate to the same packet, or whether already the transmission of a new packet has been started. This is in particular the case if the receiver is not able to receive all packets but misses some, e.g. due to interference. If the transmission employs soft handover, that means that more than one receiver tries to receive the packets, it may well be that one receiver has not been able to receive a packet, but another receiver has been able to do so. In this case a new packet can be transmitted next. The receiver which did not receive the first packet must now somehow recognize that this new packet cannot be combined with any previously received packets.
It is further possible to introduce a so called Retransmission Sequence Number (RSN) or retransmission counter:
This counter is reset (e.g. to 0) if a new packet is being transmitted, and it is incremented with each retransmission. If the receiver compares the difference in RSN with the difference in time (taking into consideration the synchronous retransmission protocol and the known time difference between retransmission), the receiver can combine the receptions if the differences match and not combine them if the differences do not match.